Diagnostic accuracy of parathyroid hormone levels in washout samples of suspicious parathyroid adenomas: A single-centre retrospective cohort study

IntroductionMinimally invasive surgery is an alternative surgical approach for primary hyperparathyroidism with less surgical trauma and anaesthesia complications. When combined with intraoperative measurement of parathyroid hormone (PTH), cure rates are exceeding 97%. Preoperative intact PTH determination in washout samples is really very useful when parathyroid lesions cannot be easily distinguished from thyroid lesions or sometimes lymph nodes. Herein, we aimed to report our institutional experience about parathyroid fine-needle aspiration (FNA) method and suggest a cut-off ratio for this purpose. MethodsIn our clinic, we performed ultrasonography (USG)-guided parathyroid FNA procedure for 131 patients diagnosed with primary hyperparathyroidism between January 2005 and January 2016. Both cytologic evaluation and intact PTH determination were performed in washout samples. Eighty-seven of the study group also had a parathyroid scintigraphy. Both demographic features and laboratory results were all recorded. ResultsMedian serum PTH level was 142 (113-197), while mean PTH washout level was 1824 (0-3953). When three of the localization techniques are compared with each other, FNA-PTH washout group had a better diagnostic accuracy (90.8%) when compared to cytology (7.92%) and MIBI (67.8%) groups. Both MIBI and FNA-PTH washout group had 100% positive predictive value (PPV) and 100% specificity. We found values greater than 436.5pg/mL for FNA-PTH washout with a sensitivity of 90.3% and specificity of 88.9% (P<0.01 and AUC 94.3 (87.8-100)) and a cut-off for FNA/serum PTH greater than 3.05 with a sensitivity of 91.2% and specificity of 89% (P=0.02 and AUC 94.5 (88.8-100)) which implicate parathyroid lesions. ConclusionAccording to the literature, PTH determination in washout samples has a specificity of 75%-100% and sensitivity of 70%-100%. This approach has better results than both cytology and scintigraphy in case of concomitant multinodular thyroid disease in experienced hands. Although there is not a definite cut-off for PTH levels in washout samples, we agree with the need of ratios rather than cut-offs in this issue.